1. Field of the Invention
This invention relates generally to a spark-ignition internal combustion engine, and more particularly to an apparatus for and a method of controlling a spark-ignition internal combustion engine of the type in which fuel is injected directly into a cylinder.
2. Related Art
There is known a conventional system (Japanese Patent Unexamined Publication No. 2-153257) in which fuel is injected directly into a cylinder by use of the air pressure. A conventional diesel engine utilizes a stratified combustion, and therefore the maximum output or power is low although the fuel consumption under a partial load is enhanced. On the other hand, a conventional gasoline engine has a drawback that although the maximum output or power is high because of a premixture combustion, the fuel consumption under a partial load is worsened because of a pumping loss.
It is an object of this invention to provide an apparatus for and a method of controlling an internal combustion engine, in which under a partial load, a pumping loss is eliminated by a stratified combustion, thereby enhancing the fuel consumption, and during a maximum-output operation, the output or power is increased by a premixture combustion, and an engine torque is controlled to improve the operability (drivability), the fuel consumption and an exhaust cleaning effect.
In order to overcome the above problem of the prior art, under a partial load, an ignition source is provided in the vicinity of a fuel injection valve, and after the fuel is injected, the mixture is ignited, and a resulting flame is caused by a spray of the fuel to spread into a cylinder, thereby effecting a stratified combustion. On the other hand, when the load increases, so that soot and so on are produced in the stratified combustion, the fuel injection is effected a plurality of times in a divided manner, and a premixture is produced within the cylinder by the former-half injection, and a flame, produced by the latter-half injection, is injected into the cylinder to burn this premixture. Thus, the premixture is burned in a short period of time. When changing the gear ratio of a transmission, the amount of the fuel is changed so that a step will not develop in a torque.
When the amount of injection of the fuel is small as in a partial-load operation, the initiation of the injection and the ignition timing can be relatively close to each other, and therefore the fuel is not so much spread within the cylinder, and the combustion (stratified combustion) takes place in a relatively narrow range. In accordance with the increase of the load, the initiation of the injection is made earlier, so that the range of formation of the mixture (premixture) increases, and a premixture combustion takes place, thereby increasing the produced torque.
In accordance with the drive torque, the gear ratio of the transmission is selected, and if the drive torque need to be further increased, the gear ratio of the transmission is increased. When changing the gear ratio, the fuel injection amount is controlled so that the drive torque will not be varied. The fuel is injected into the combustion chamber of the engine by a fuel injection valve having a port (opening) therein, and therefore the fuel will not deposit on an intake manifold and other portions, and the speed of inflow of the fuel is high, and the engine torque can be controlled with a good response. The air/fuel ratio can be set to a large value, and therefore a throttle valve opening degree can be increased to reduce a pumping loss, thereby enhancing a fuel consumption. Moreover, since the air/fuel ratio can be increased, the amount of CO and HC in the exhaust gas can be reduced.